The present invention relates to a fluorescent display device and, more particularly, to a fluorescent display device with an improved structural relationship between a filament supporter and a base.
A fluorescent display device for use in display devices for digital measuring instruments, telephones, communications apparatus, etc., is constructed as shown in FIG. 1.
Here, a signal line 2 composed of a conductive metal such as aluminum (A1), is disposed on a glass substrate 1 that defines a vacuum vessel together with cover plate 1a, and an insulation layer 3 is disposed on signal line 2 for the protection thereof. Conductive segment layers 4 are disposed on insulation layer 3 in a predetermined pattern, and a fluorescent layer 5 is disposed each conductive segment layer 4. Through-holes 3a are arranged below conductive layer 4 so that conductive layer 4 and signal line 2 are electrically connected via through-holes 3a. Moreover, a grid 7 for controlling thermopic flow and filaments 6 for emitting thermal electrons are installed at different levels above fluorescent layer 5.
FIG. 2 is a schematic, perspective view showing the conventional fluorescent display device having filaments 6 shown in FIG. 1. Two bases 9 of a predetermined width are secured opposite ends of substrate 1 spaced from each other by a predetermined interval, and each supporter 8 to which filaments 6 are welded and secured is welded to one of the bases 9. Supporters 8 and bases 9 have position-setting holes 8a and 9a for setting the exact positions for welding. Also, substrate 1 has position-setting patterns corresponding to position-setting holes 9a of the bases 9.
In the conventional fluorescent display devices constructed as above, the interval between the two bases is of most importance in supplying the filaments with uniform tension. Accordingly, when manufacturing a fluorescent display device, the filament length should be determined according to the interval between the two supporters. Therefore, if the two supporters fixed on the base are not kept parallel, or the interval is greatly different from the predetermined interval, the tension of filaments is insufficient or excessive. When the substantial tension of the filaments is lower than the predetermined tension, the filaments are not pulled tight, but droop towards the substrate. On the contrary, if the tension of filaments greatly exceeds the predetermined tension requirement, the filaments impose an excessive load on the supporters, so that the supporters may be deformed.
To overcome the problems due to the improper interval between the supporters, position-setting holes are arranged on the bases and the supporters, for their exact matching. In the conventional fluorescent display devices, as described above. since the position-setting holes are located at exact positions on the supporters and bases for the consistency therebetween, a variation in supporter size leads to a change of the size of the bases. Further, position-setting holes to be formed on the bases and supporters must be consistent with one another.
The fluorescent display device as described above has a disadvantage in that the supporters and bases have a limited application range. That is, a variety of supporters of different sizes (also having different intervals between position-setting holes) cannot be secured onto a base of any particular size. Therefore, the supporters of a particular specification and corresponding bases should be corelated.
Therefore, due to the above requirements, the bases and supporters of a particular specification must provided in correspondence with the specification of the fluorescent display device, which is cumbersome.